Spark plug



Nov. 22, 1932.

J. D. FORSYTH SPARK PLUG FiledApril-B; 1930 n ll Patented Nov. 22, 1932 PATENT OFFICE JAMES D. FORSYTH, OF TONAWANDA, NEW YORK SPARK PLUG Applicationv filed April 8, 1930. Serial No. 442,653.

This invention relates to improvements in the spark plugs employed for igniting the explosive mixture of internal combustion engines.

One of its objects is to provide a simple and efficient plug of this character which will produce a spark of maximum intensity, which will not foul, and which will result in more power with a less consumption of fuel.

A further object of the invention is the provision of a spark plug having a multiple of sparking points which are readily replaceable and which are adjustable to vary the intensity of the spark.

In the accompanying drawing Figure 1 is a side elevation of my improved spark plug. Figure 2 is a central longitudinal section thereof. Figure 3 is a similar view but showing a different adjustment of the spark elements. Figure 4: is a bottom plan view of the plug. Figure 5 is a horizontal section taken on line 5-5, Figure 3. Figure 6 is a detached perspective view of the auxiliary electrodes.

Similar characters of reference indicate corresponding parts throughout the several views.

In its preferred form, my spark plug includes a metallic tubular casing 10 having an externally threaded attaching stem 11 at its lower end for securing it to the head of the engine, and an internally threaded portion 12 at its upper end terminating in an upwardly-facing annular seat or shoulder 13. Extending through the casing is an insulating core 14 provided intermediate its ends with a collar 15 bearing at its lower side on said shoulder 13, while its upper side is engaged by a clamping nut 16 threaded into the upper end of the casing, as shown in Figures 2 and 3, suitable packing rings 17 being interposed between the respective faces.

The numeral 18 indicates the main electrode of the plug which extends centrally through the core 14 and is firmly secured thereto at its upper end where it terminates in a threaded post or projection 19 for re ceiving the customary nut 20 for clamping the terminal wire 21 thereto. Applied to the lower end of the core and surrounding the main electrode are a plurality of mixiliary electrodes, indicated generally by the numerals 22, 23, which are securely fastened to the core and which are renewable.

trode 22 having an attaching shank 24 pref.- erably formed by bending the wire upon ltself and adapted to be inserted in an opening 25 in the .core 14, the lower end of the shank terminating at one end in an upright leg or round contact terminal 26 engaging a groove 27 in the outer side of said core and adapted in one position .of the core to contact with the surrounding wall of the casing 10 and thus be grounded thereto. The other end of the electrode-shank 24 is formed into a substantially arcuate terminal 28.. The auxiliary electrode 23 is substantially the same as that of the companion one, having an attach- 7 mgshank 29 fitted in. an opening 30 in the core, an arcuate terminal 31 extending toward the companion terminal 28 and spaced therefrom to format spark gapyand a radial- Iy-disposed terminal .32 extending toward the main electrode and spaced therefrom to form a spark gap.

With the parts in the position depicted in Figures 2 and 4, the electrode-terminal 26 is grounded to the casing 10, thus providing two 3 spark gaps, one between the auxiliary electrode-terminals 28., 31 and the other between the main electrode 18 and the auxiliary electrode-terminal 32.

In order to reliably hold the auxiliary eleccesses 33 formed at the upper ends of the shank-openings 25, 30. If desired, these recesses may be filled in with a suitable cement. I The holes in the core through which the various electrodes pass are somewhatlarger in diameter than the latter to allow for the expansion of the electrodes when they become hot. i For the purpose of varying the intensity of the spark as well .as increasing the number ofspark gaps, the lower ends of the -contigu-.

These auxiliary electrodes are pref 55 erably made .of a wire conductor, the elecp the core in place.

ous faces of the casing 10 and core 14 are eccentrically disposed and the core is rotatable within the casing to bring the ground terminal 26 of the auxiliary electrode 22 out of contact with the casing-bore and provide a spark gap therewith. As shown in Figures 4 and 5, this result is accomplished by providing the lower end of the casing with an cecentrically-bored portion 34, so that upon loosening the clamping nut 16 and turning the core, the terminal 26 on the latter may be brought either in contacting relation with such bore to form a ground contact or it may be set in a position to provide a variable spark gap between such terminal and the eccentric-shaped inner wall of the casing. When the core is set in the position desired, the clamping nut is tightened to firmly hold To facilitate the setting of the core for the desired spark intensity, the projecting upper end of the core has a gage mark thereon which is adapted to be brought in line with any one of a series of annular markings 36 applied to the top face of the casing 10. Thus, when it is desired to ground the terminal 26 to the casing, the core is turned to bring its gage mark opposite 0 on the casing; similarly; if an additional sparking point is desired, the core is turned to bring its mark opposite either the 5, 10 etc. marking on the casing, depending on the intensity of the spark desired.

While manifestly simple. compact and inexpensive in construction, this spark plug is efiici-ent in operation and'is readily adapted to varying conditions to intensify the sparking capacity of the plug.

I claim as my invention 1. A spark plug, comprising a metallic casing, an insulating core adapted to turn therein and having its lower end in eccentric relation to the casin g-bore, a main electrode extending through said. core, and a plurality of auxiliary electrodes applied to said core about the main electrode to form a plurality of spark gaps, the innermost terminal of said auxiliary electrodes being in sparking relation to the main electrode and the outermost terminal of said auxiliary electrodes being disposed between the contiguous faces of the casing and the core, said outermost terminal being adapted to form a ground contact with the casing in one position of the core and to form a spark gap therewith in another position of the core.

2. A spark plug, comprising a metallic casing having an internally threaded upper end and an eccentric bore at its lower end, an insulating core extending axially through said casing and revolvable therein, a clamping nut engageable with the threaded end of the casing to hold the core against rotation, a main electrode extending through said core, and a plurality of auxiliary electrodes applied to said core about the main electrode, each of said auxiliary electrodes including a pair of terminals, one terminal of each pair being disposed opposite each other to form a spark gap, the remaining terminal of one pair being disposed in sparking relation to the main electrode and the remaining terminal of the other pair being disposed between the contiguous faces of the casing and the core, said last named terminal being adapted to form a ground contact with the casing in one position of the core and to form a spark gap therewith in another position of the core.

JAMES D. FORSYTH. 

